Users of multiple computer systems are able to share data through the use of many types of communications systems. Such communications systems are known as "networks", examples of which include Local Area Networks (LANs), Wide Area Networks (WANs), and Metropolitan Area Networks (MANs). As the number of networks in each office building or manufacturing plant has increased, there has arisen a desire to interconnect multiple network devices at a central location. This central location is typically a "wiring closet". Networking hubs, or "hubs", are used in wiring closets to provide a central connection point for multiple network devices, such as bridges, routers, terminal servers, repeaters and probes.
Typically, a hub includes several attachment slots to hold line cards. Each line card contains one or more network devices attached to the hub. Internal data path resources within the hub are used to pass data between the multiple line cards. Each line card includes zero or more front panel connections, which are used to connect the line card to one or more external networks on which the line card operates. The external networks connected with the line card may be one of a variety of network types, such as Ethernet, Token Ring (IEEE 802.5), Fiber Distributed Data Interconnect, Asynchronous Transfer Mode, Wide Area Network Links, or proprietary buses.
A first disadvantage of existing hub designs is that the capabilities and characteristics of each type of line card must be stored a priori in a management agent for the hub. In such existing designs, when a line card is attached to the networking hub, the management agent reads the product ID, or "type" of the line card. Based on the type of the line card, the management agent determines how the line card can use the internal data path resources to pass data to other line cards attached to the hub. The management agent in such existing systems therefore requires a priori knowledge of what shared data path resources are accessible to all line card types, and the methods by which each line card type can use those accessible shared data path resources.
For reasons of economy, all line card types do not include circuitry to access all the shared data path resources in the hub. Similarly, new line card types will include circuitry to access only a subset of those shared data path resources accessible to previous line card types. In existing designs, the hub management agent must know what shared data path resources each new line card type can access, in order to pass information to and from the new line card, and in order to connect the new line card with other line cards attached to the networking hub. Therefore, in existing systems, whenever a new type of line card is developed, the management agent must be upgraded to include the necessary a priori information regarding the characteristics and capabilities of the new line card type. Upgrading is typically accomplished through loading of a new firmware image. Such procedures are time consuming, inconvenient and costly to the user of the networking hub.
Other existing systems dedicate specific shared data path resources within the hub for corresponding specific predetermined networking technologies. For example, such a system might have a first data path for a first communications protocol, and a second data path for a second communications protocol. When the capacity of the first data path was exhausted, no further line cards using the first communications protocol could be attached with the hub without physically installing a new shared data path, supporting the first communications protocol, into the hub. Without the physical upgrade the management agent in the networking hub cannot connect a new line card using the first communications protocol to other line cards attached to the networking hub. The requirement of a physical upgrade to accommodate a particular combination of line cards is inflexible and therefore undesirable.
Other examples of existing systems use dip switches on each line card to indicate how the line card is to communicate with the management agent within the hub. Such systems are not remotely manageable, often requiring that the line card be physically removed from the hub to modify the dip switch values. Physically removing a line card is undesirable, as it may require bringing power down on the hub, thus impacting the operation of other line cards installed in the hub.
There is therefore a need for a new system for interconnecting network devices, that efficiently supports multiple external network types, and is capable of supporting future generations of network line cards, where the new lines cards may have new capabilities and characteristics, without upgrade of the management agent in the networking hub or physical modification of the networking hub. The new system should support remote management of line cards installed in the hub, and satisfy requests to logically connect line cards installed in the networking hub without disturbing existing connections.